/Engine/Source/Runtime/Core/Public/Misc/FrameTime.h
Structure representing a time by a context-free frame number, plus a sub frame value in the range [0:1) Conversion to and from time in seconds is achieved in combination withFFrameRate. Only the frame number part of this representation can be negative, sub frames are always a positive value between the frame number and its next logical frame
struct FFrameTime
FFrameNumber
FrameNumber